Solar collector having a spaced frame support structure with a multiplicity of linear struts

ABSTRACT

The present invention relates to a solar energy collector suitable for use in a solar energy collection system. The solar energy collection system includes the collector, a stand that supports the collector and a tracking system that causes the collector to track movements of the sun along at least one axis. The collector includes one or more reflector panels, one or more solar receivers, and a support structure that physically supports the reflector panels and solar receivers. Some designs involve a reflector panel that has a compound curvature. That is, the reflector panel has a convex shape along one direction and a concave shape in another direction. In another aspect of the invention, the collector includes a space frame support structure.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present invention claims priority to U.S. Provisional ApplicationNo. 61/362,591, entitled “Optimized Solar Collector,” filed Jul. 8,2010, which is incorporated herein in its entirety for all purposes.

FIELD OF THE INVENTION

The present invention relates to solar technologies. More specifically,the present invention relates to various collector, reflector andsupport structure designs for use in concentrating photovoltaic systems.

BACKGROUND OF THE INVENTION

Typically, the most expensive component of a photovoltaic (PV) solarcollection system is the photovoltaic cell. To help conservephotovoltaic material, concentrating photovoltaic (CPV) systems useminors or lenses to concentrate solar radiation on a smaller cell area.Since the material used to make the optical concentrator is lessexpensive than the material used to make the cells, CPV systems arethought to be more cost-effective than conventional PV systems.

One of the design challenges for any CPV system is the need to balancemultiple priorities. For one, a CPV system requires a support structurethat arranges the optical concentrators and the photovoltaic cells suchthat incoming sunlight is efficiently converted into electricity. Thissupport structure should also accommodate a tracking system and providefor the adequate dissipation of heat. Another consideration is the costof manufacturing, installing and repairing the CPV system. Existing CPVdesigns address these issues in a wide variety of ways. Althoughexisting CPV systems work well, there are continuing efforts to improvethe performance, efficiency and reliability of CPV systems.

SUMMARY OF THE INVENTION

One aspect of the present invention relates to a photovoltaic solarenergy collector suitable for use in a solar energy collection systemthat includes a stand and a tracking system. The solar collectorincludes one or more reflector panels, one or more solar receivers, anda support structure. In this aspect of the present invention, thereflective panel has a compound curvature. That is, the reflective panelhas a concave shape in one direction that is suitable for directingincident light to form a flux line on the solar receivers. Thereflective panel also has a slightly convex shape in another direction.This compound curvature offers various advantages. For example, gaps mayform in or between the reflector panels that can cause the flux line onthe solar receivers to be non-continuous. This can reduce the efficiencyof the photovoltaic cells. The convex curvature, by spreading out thelight reflected by each reflector panel, can help wash out such gaps andmaintain the continuity of the flux line making the flux line morelongitudinally uniform As a result, the photovoltaic cells on thecollector receive more uniform exposure to reflected sunlight.

The present invention contemplates a large assortment of collectordesigns. Some embodiments involve an A-type design, where the reflectivepanels curve inward towards one another and reflect light outward tosolar receivers that are positioned at the periphery of the collector.Still other embodiments involve a U-type design, where the reflectivepanels curve outward away from one another and reflect light inward tosolar receivers that are positioned over a central region between thetwo reflective panels. Some designs involve extended versions of eitherof these designs, in which a larger number of reflector panels aremounted onto a common base platform and solar receivers are positionedon the backsides of the reflector panels. The present invention alsocontemplates a power generation plant where solar collector rows areformed from multiple collectors that are longitudinally attached andarranged to pivot in tandem to track movements of the sun.

In another aspect of the invention, the support structure for the solarcollector is a space frame. That is, the support structure is formedfrom interlocking linear struts that are connected at nodes. There arelarge apertures and spaces between the struts that allow the free flowof air through the space frame, thereby reducing the wind load on thesolar collector. The space frame support structure includes receiversupport struts and reflector support struts. In various implementations,the receiver and reflector support struts are integrated into a unitaryspace frame support structure. That is, struts and nodes are arrangedsuch that the loads from the reflectors and receivers are not carriedentirely by the struts that are immediately attached to them. In variouspreferred embodiments, these loads are instead dispersed more widelythrough the space frame support structure.

There are a wide variety of ways of arranging the struts and nodes ofthe space frame support structure. Some implementations involve the useof longerons that extend parallel to one another along the longitudinalaxis of the solar collector. Nodes are positioned at various pointsalong each longeron. Multiple struts extend diagonally outward fromthese nodes to provide additional structural support for the solarcollector. In some embodiments, there is a upper longeron that extendsdown the middle of the collector. Solar receivers may be attached atvarious points along the upper longeron. In various other embodiments,solar receivers are instead attached with side longerons that arelocated at the periphery of the collector. Preferably, the space framesupport structure is arranged to be highly flexible. That is, ratherthan being tailored to reflector panels and/or solar receivers ofparticular shapes and sizes, the space frame support structure isarranged to accommodate various types of reflector panels and solarreceivers such that minimal additional work is required to attach themto the space frame support structure

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and the advantages thereof, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings in which:

FIGS. 1A and 1B are diagrammatic perspective and cross-sectional viewsof a solar collector according to a particular embodiment of the presentinvention.

FIG. 2A is a diagrammatic side view of a reflector panel with a convexshape according to a particular embodiment of the present invention.

FIG. 2B is a diagrammatic side view of a reflector made of multiplereflector panels according to a particular embodiment of the presentinvention.

FIG. 2C is a diagrammatic side view of the reflector panel illustratedin FIG. 2A.

FIGS. 3A-3D are diagrammatic cross-sectional views of solar receiversand reflector panels according to various embodiments of the presentinvention.

FIGS. 4A and 4B are diagrammatic perspective and cross-sectional viewsof a collector unit according to a particular embodiment of the presentinvention.

FIGS. 5A-5C and 6A-6C are diagrammatic cross-sectional views of variouscollectors that are formed from different arrangements of the collectorunits illustrated in FIGS. 4A and 4B.

FIGS. 7A-7D are diagrammatic cross-sectional and perspective views of asolar collector with a space frame support structure in accordance withvarious embodiments of the present invention.

FIGS. 8A and 8B are diagrammatic perspective views of a connectorsuitable for use in a space frame support structure according to aparticular embodiment of the present invention.

FIGS. 9A and 9B are diagrammatic cross-sectional and perspective viewsof a solar collector with a space frame support structure in accordancewith another embodiment of the present invention.

FIGS. 10A and 10B are diagrammatic cross-sectional and perspective viewsof a reflector panel according to a particular embodiment of the presentinvention.

FIG. 11 is a diagrammatic perspective view of multiple solar collectorsthat are arranged to form a solar collector row in accordance with aparticular embodiment of the present invention.

FIG. 12 is a diagrammatic cross-sectional view of a solar collector thatis suitable for pivoting around an axis in accordance with a particularembodiment of the present invention.

FIGS. 13A and 13B are diagrammatic cross-sectional and perspective viewsof a solar collector with a support cable in accordance with aparticular embodiment of the present invention.

In the drawings, like reference numerals are sometimes used to designatelike structural elements. It should also be appreciated that thedepictions in the figures are diagrammatic and not to scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates generally to concentrating photovoltaicsystems. The assignee for the present application, Skyline Solar, Inc.,has received multiple patents related to such technologies, such as U.S.Pat. No. 7,709,730, entitled “Dual Trough Concentrating SolarPhotovoltaic Module,” filed Apr. 10, 2008, which is hereby incorporatedby reference in its entirety for all purposes and is hereinafterreferred to as the '730 patent.

The '730 patent describes various solar collector designs that involve atrough-shaped reflector that directs incident sunlight to a string ofphotovoltaic cells. The described designs work well for manyapplications. During the course of installing, manufacturing andoperating solar energy collection systems, however, the assignee hasidentified various areas in which the designs could be further improved.For example, ordinary wear and tear can form gaps in the reflector. Thiscan skew the reflection of light by the reflector and may reduce thecollection of solar energy. It would also be desirable to develop animproved support structure for the collector that is resilient,lightweight and cost-effective. The present application contemplates awide variety of design concepts relating to collectors, supportstructures, reflector panels, power plants and tracking systems thataddress these and other concerns.

Initially, with reference to FIGS. 1A and 1B, a concentratingphotovoltaic solar collector 100 according to a particular embodiment ofthe present invention will be described. The solar collector includesmultiple solar receivers 102 and reflector panels 104 that each have acompound curvature. The reflector panels 104 are arranged in one or morerows that extend along the longitudinal axis 106. Each row includesmultiple, adjacent reflector panels that cooperate to form a reflector108 with a substantially continuous reflective surface. The solarreceivers 102 each have at least one photovoltaic cell 118 and arearranged to form a string of photovoltaic cells 118. A space framesupport structure 110 physically supports the reflector panels 104 andthe solar receivers 102. A tracking system causes the collector to pivotto track the movements of the sun. FIG. 1B is a diagrammaticcross-sectional view of the solar collector 100 illustrated in FIG. 1A.

Foundation settling, differential thermal expansion, and mechanicaltolerances in the manufacturing and installation of a reflector cancause undesirable gaps to open up between the reflector panels 104 inthe reflector. If the reflective surface becomes non-continuous, thenthe flux line that forms on the string of photovoltaic cells 118 mayinclude gaps and become non-continuous as well. As a result, theexposure of the photovoltaic cells to concentrated sunlight will be lessuniform, which can substantially reduce the cell strings' efficiency.

Various embodiments of the present invention relate to reflector panels104 that are designed to address this problem. More specifically, eachreflector panel 104 incorporates two different curvatures along twodifferent axes. Along a plane defined by an x axis 114 and a y axis 112,the reflector panel 104 has a concave shape. Along another axis (e.g.,the longitudinal axis 106, which goes into the page in FIG. 1B and isperpendicular to the x-y plane), the reflector panel has a convex shape.The concave shape is arranged to direct incident light 116 to the solarreceivers 102, as shown by the arrows in FIG. 1B. The convex shapecauses the light that is reflected by the panel 104 to be reflected in awider arc along the longitudinal axis 106. That is, the convex shape ofeach panel 104 forms a wider flux line (as measured along thelongitudinal axis 106) than would be the case if the panel were flatalong the longitudinal axis. As a result, gaps in the flux line that areformed by gaps in the reflective surface are covered up or washed away.This can produce a more continuous, uniform flux line, which contributesto greater cell string efficiency.

Another notable feature of the collector 100 illustrated in FIGS. 1A and1B is the space frame support structure 110 that supports the solarreceivers and reflector panels. The space frame support structureincludes multiple linear struts 120 that are connected with nodes 122 toform repeating geometric shapes (e.g., triangles, pyramids,tetrahedrons, etc.) This arrangement offers various advantages. For one,the large apertures in between the struts 120 allow the free flow of airand reduce wind load on the collector. The use of repeating components,such as the nodes 122 and the struts 120, can streamline themanufacturing, installation and repair of the space frame. Thelongitudinal period of the repeating geometric pattern does not have tocorrespond to the longitudinal length of either a receiver or reflectorpanel, allowing flexibility in receiver and reflector panel design.

Additionally, the space frame support structure 110 in FIGS. 1A and 1Bis designed to operate as a unitary structure. That is, struts thatsupport different components of the collector are interlocked with therest of the space frame and are therefore more stable and resistant tostress and bending. In the illustrated embodiment, for example, thesupport for the solar receivers is not a single, isolated column orpedestal. Instead, it is arranged in the form of multiple receiversupport struts 124 that are connected to nodes 122 that in turn connectwith and help support other struts and components, such as the reflectorpanels 104. The struts are arranged to firmly anchor importantcomponents of the collector within the support structure, reduce oreliminate bending, and form multiple paths through which mechanicalloads may be dispersed.

The struts 120/124 and nodes 122 of the space frame structure may take avariety of forms. By way of example, the struts 120/124 may becylinders, tubes, pipes, roll formed steel sections, hot rolled steelsections, etc. Many of the struts may have similar circumferences andmay be formed using the same or similar manufacturing processes. Thestruts 120/124 may be connected with one another at the nodes 122 in anysuitable manner, including the use of welding, metal clinching,adhesive, rivets, bolts and nuts, fasteners, etc. In some embodiments,the nodes 122 include connectors that are formed from extruded aluminum,sheet metal, forged steel spheres or other materials.

Preferably, the space frame support structure is designed to becompatible with many different types of reflector panels and solarreceivers. In the illustrated embodiment, for example, the struts 120underneath the reflector panels 104 form a stable base platform forphysically supporting the reflector panels. This base platform is notarranged to be compatible only with a reflector panel of a highlyspecific length and curvature. That is, the base platform is notnecessarily form fitted to the dimensions of a particular reflectorpanel. Instead, with minimal modifications (e.g., the drilling of holes,the securing of fasteners, etc.), the base platform can be configured toaccommodate reflector panels of varying lengths, shapes and/orcurvatures as long as the reflector panels, when lined up along thelength of the collector, generally fit the dimensions of the space framesupport structure.

The reflector panels 104 and solar receivers 102 may be arranged in awide variety of ways, depending on the needs of a particularapplication. In the illustrated embodiment, for example, the reflectorpanels 104 form a U-like shape. The solar receivers 102 are arranged intwo adjacent rows that are positioned higher and over a region that isbetween the reflectors. The two rows of solar receivers 102 supportstrings of photovoltaic cells 118 that face away from one another andtowards the reflectors 104. When sunlight is incident on one of thelongitudinally extended reflectors 104, a longitudinally extended fluxline is formed on the corresponding string of photovoltaic cells 118. Inanother embodiment, the solar receivers 102 are positioned at theperiphery of the collector 100, and the reflector panels 104, ratherthan directing incident light inward towards the center of the collector100, instead direct light outward towards the periphery of the collector100.

The reflector panels 104 may be made from any suitable reflectivematerial. For example, metalized glass and aluminum work well asmaterials for the reflector panels 104. Each solar receiver 102 mayinclude or be attached with a wide variety of components, such as a heatsink, fins, base plates, etc. In some embodiments, the heat sink and/orthe solar receiver include a fluid conduit. The sunlight that isreflected onto the solar receivers 102 may be used to heat a liquid thatis flowing through the fluid conduit. A wide variety of possible solarreceiver, heat sink and fin designs are described in U.S. Pat. No.7,820,906, entitled “Photovoltaic Receiver”, filed May 20, 2008, andU.S. patent application Ser. No. 12/340,379, entitled “Solar Receiver,”filed Dec. 19, 2008, which are hereby incorporated in their entirety forall purposes.

Referring next to FIGS. 2A and 2C, a reflector panel 200 with a compoundcurvature according to a particular embodiment of the present inventionwill be described. The reflector panel has a convex shape in onedirection and a concave shape in another. FIGS. 2A and 2C arediagrammatic side views of the reflector panel 200 that show its convexshape. The convex shape is defined in part by a distance d, whichmeasures the amount of maximum displacement of the convex shape relativeto a flat reference surface, and a longitudinal length l. While thereflector panel in FIGS. 2A and 2C is shown as having a single convexbow, the reflector panel may also include multiple convex regions. Insome embodiments, these convex regions may be interspersed with concaveand/or flat regions. When properly utilized in a suitable collector, theconvex shape of the reflector panel 200 may substantially improve theefficiency and performance of the collector.

As discussed earlier in connection with FIG. 1A, the present inventioncontemplates collector designs where multiple reflector panels 200 arearranged together along a longitudinal axis 106 to form a reflector 202with a curved reflective surface. The reflective surface receivesincident sunlight and directs it to a string of one or more photovoltaiccells. As a result, a flux line (e.g., a strip or band of concentratedillumination formed by the reflected light) is formed on the string ofcells. The shape and dimensions of the flux line are defined in largemeasure by the shape of the reflector panel 200.

When the reflector panels are flat along the longitudinal axis, the fluxline will tend to mirror the continuity of the reflective surface. Thatis, if the reflective surface is continuous, then the flux line tends tobe continuous. However, if the reflective surface has gaps, then theflux line will also tend to have gaps (e.g., portions of the cell facewithin the periphery of the flux line that do not receive light from thereflective surface.)

Since the movement of the sun throughout the day causes light to bereflected by the reflector panels at a variety of angles, the effect ofany gap between the reflector panels may appear almost anywhere alongthe length of the cell string. That is, a gap between two reflectorpanels could prevent a central portion of one of the photovoltaic cellsfrom being illuminated by reflected light. This can substantially reducecell efficiency, particularly when the cells are electrically connectedin series. Unfortunately, it is not uncommon for gaps to develop betweenthe reflective panels that make up the reflective surface. The gaps mayarise due to errors in manufacturing, installation, operation orconstant thermal expansion and contraction.

The convex shape of the reflector panels 200 helps to eliminate gaps inthe flux line. FIGS. 2A and 2C illustrate how incoming sunlight 204 isreflected when it strikes the convex curvature of the reflector panel200. The reflected light tends to spread or fan out from the reflectorpanel 200. Depending on the direction of the incoming sunlight, thereflected light may spread out on both sides of the reflector panel(e.g., as in FIG. 2A, where the incoming light is perpendicular to thelongitudinal axis 106) or more to one side (e.g., as in FIG. 2C, wherethe incoming light is coming in at an angle.) Generally, the reflectedlight forms a wider flux line (along the longitudinal axis) then wouldbe the case if the reflector panel 200 were flat.

Referring next to FIG. 2B, a reflector 202 made of the reflective panels200 illustrated in FIGS. 2A and 2C will be described. The reflectivepanels 200 are arranged adjacent to one another along a longitudinalaxis 106. Collectively, the reflective panels 200, each with length l,form a reflector 202 with a length L. The reflector includes multipleconvex shapes, where each reflective panel 200 forms one of the concaveshapes. When multiple reflector panels are arranged together in thismanner, the aforementioned spreading out of the reflected light washesout or eliminates gaps in the flux line that would be normally be causedby gaps between the reflector panels. As a result of the washing outeffect, the flux line on the photovoltaic cells is more continuous anduniform.

Various designs involve a reflector 202 where at least two or moreadjacent reflector panels 200 of the reflector 202 have the same concaveshape (e.g., as seen in FIG. 2B.) In some embodiments, the convex shapeof each reflector panel 200 is also substantially symmetrical and theaxes of symmetry 206 of the convex shapes of the reflector panels 200run substantially parallel to one another. This arrangement promotes thespreading of light on both sides of each reflector panel 200, which canbe particularly effective in washing out the effects of gaps between thereflector panels 200.

It should also be appreciated that the amount of convex curvature ineach reflector panel 200 of a reflector 202 need not be the same. By wayof example, the end reflector panels 200 shown in FIG. 2B may have agreater amount of convex curvature than the other reflector panels,since there may be a larger gap between these reflector panels andreflector panels on a longitudinally adjacent solar collector than thegap between adjacent reflector panels on the same solar collector.

The convex curvature of the reflector panel 200 may be different nearthe lower edge of a reflector panel 200 (e.g., the displacement d may begreater or lower) than it is near the upper edge of the reflector panel200. The variation in convex curvature may be inversely related to thedistance variation between the reflector panel and receiver. Inparticular the lower edge of the reflector panel may be closer to thereceiver than the upper edge of the reflector panel. The convexcurvature may thus be larger near the lower edge of the reflector paneland smaller near the upper edge of the reflector panel. This variationin convex curvature across the reflector panel may result in alongitudinally more uniform flux line.

It should be noted that in the figures, the degree of convex curvatureis exaggerated for the purpose of clarity. Generally, the concavity ofthe reflector panel 200 is significantly greater than the convexity ofthe reflector panel (e.g., the concave radius of curvature may be 20 ormore times less than the convex radius of curvature.) Note that asmaller radius of curvature corresponds to more curvature or a higherdegree of concavity or convexity. Various embodiments involve areflector panel with a convex radius of curvature for the reflectorpanel 200 that is approximately between 50 and 70 m, although the degreeof curvature may be lower or higher for other implementations. Inparticular reflector panels 200 having a longer length in thelongitudinal direction may generally have a larger convex radius ofcurvature.

Referring next to FIGS. 3A-3D, solar receiver and reflector arrangementsaccording to various embodiments of the present invention will bedescribed. FIG. 3A is a diagrammatic cross-sectional view of anarrangement 300 including a reflector panel 302 and a solar receiver304. From this vantage point, the reflector panel 302 has a concaveshape. The solar receiver includes one or more photovoltaic cells 306.The reflector panel 302, whose optical aperture has a width w, isarranged to direct incident sunlight to the solar receiver.

This arrangement 300 offers various advantages. For one, the solarreceiver is positioned outside of the optical aperture 308 of thereflector panel 302. In the illustrated embodiment, for example, thesolar receiver 304 (and any associated support structure) does notdirectly overlie the reflector panel 302 and does not shade thereflector panel 302 during the normal operation of the solar collector.This lack of shadowing helps maximize the energy output of thephotovoltaic cells 306 by increasing the amount of light that isreflected to the cells.

Also, the arrangement 300 allows the reflector panel 302 to bepositioned relatively close to the solar receiver 304. If the reflectedlight has to traverse a shorter distance between the reflector and thesolar receiver, less precision is required from the collector and thetracking system. By way of example, assume that f_(avg) is the averagedistance between all the points on the surface of the reflector panel302 and the photovoltaic cell 306. Various collector designs arrange thesolar receiver 304 and the reflector panel 302 such that f_(avg) isapproximately between 0.5 m and 1.5 m, although larger or smaller valuesof f_(avg) may be used.

The size and shape of the reflector panel 302 may be adjusted so thatlight is concentrated on the photovoltaic cell 306 to the desireddegree. The optical concentration factor, which may be defined as theratio of the width w_(r) of the reflector panel 302 to the height of thephotovoltaic cell h, relates to the average increase in the sunlightintensity as compared to the intensity of the incoming sunlight 315.Since the photovoltaic cell 306 is typically the most expensivecomponent of a collector, if a larger reflective surface can be used tofocus light on a smaller photovoltaic area, there may be substantialcost savings. In various embodiments of the present invention, thereflector panels and solar receivers of the collector are arranged tohave an optical concentration factor of approximately between 5 and 50.

The efficiency of the solar collector may also be improved bycontrolling the width w_(s) of the solar receiver. If the receiver widthw_(s) along the x axis is reduced relative to the width w of the opticalaperture, a greater proportion of the total collector area can be takenup by the reflectors, which in turn results in the direction of morelight to the photovoltaic cells of the collector. Some implementationsof the present invention contemplate a receiver width that is less thanapproximately 10%, 15% or 20% of the optical aperture width w.

Referring next to FIG. 3B, a variation on the solar receiver andreflector arrangement of FIG. 3A according to another embodiment of thepresent invention will be described. The concave reflective surface ofFIG. 3A, instead of being formed by a single reflector panel, is insteadformed by multiple reflector panels 310 a/310 b/310 c that are arrangedside by side. That is, the reflector panels 310 a/310 b/310 c formstrips that extend substantially parallel to one another down thelongitudinal length of the collector. For some applications, it is morecost-effective to manufacture a larger amount of smaller reflectorpanels as opposed to a smaller amount of larger ones.

Although three separate reflector panels are shown, it should beappreciated that the concave reflective surface may be formed fromalmost any number of reflector panels. The reflector panels may beattached in any suitable manner. In the illustrated embodiment, forexample, the edges of the reflector panels 310 a/310 b/310 c overlap oneanother and can be secured together using any suitable means, such as afastener, a bolt, an adhesive, a latch, welding, etc. Variousimplementations involve multiple reflective panels that are each curvedsuch that they cooperate to form a single reflective surface with aconcave and/or parabolic shape. In other embodiments, each reflectivepanel 310 a/310 b/310 c is substantially flat in the x-y plane, but areangled such that they collectively approximate a single concave orparabolic curve. They may have a slight convex curvature along thelongitudinal axis.

Referring next to FIGS. 3C and 3D, a solar receiver and reflectorarrangement 320 according to another embodiment of the present inventionwill be described. In FIGS. 3A-3B, the solar receivers 304 weregenerally positioned higher than the highest edge of the associatedreflector panel 302. By contrast, FIG. 3C illustrates a solar receiver304 that is positioned at a height than is in between the heights of thelower and upper edges 312 and 314 of the reflector panel. Since thesolar receiver 304 is more centrally located relative to the reflectorpanel 302, the angles of incidence (in a plane defined by the x axis 114and the y axis 112) of reflected light on the cell face may be smallerthan in other designs where the solar receiver 304 is positionedparticularly low or high relative to the reflector panel 302. A reducedangle of incidence may cause less of the light to be reflected off theface of the cell, which helps increase the collection of solar energy.In the illustrated embodiment, the face of the photovoltaic cell 306 onthe solar receiver 304 is substantially perpendicular to the opticalaperture 308 of the reflector panel 302, although in other embodimentsit may be tilted.

Referring now to FIG. 3D, possible arrangements of a reflector panel anda solar receiver according to various embodiments of the presentinvention are described. FIG. 3D illustrates a parabolic curve 322,which represents the shape of one or more possible reflector panelsalong a plane defined by a y axis 112 and a x axis 114. The focus 324indicates a location of a photovoltaic cell where these possiblereflective panels direct incident sunlight. A first portion 326 of theparabolic curve approximates the shape and the position of the reflectorpanel in FIG. 3A. A second portion 328 of the parabolic curveapproximates the shape and position of the reflector panel in FIG. 3C.Any number of reflector panels can be imagined that have reflectivesurfaces that conform substantially with the parabolic curve, which isarranged to direct substantially all incoming incident sunlight to thefocus 324. A review of FIG. 3D indicates that the degree of curvature ofa reflector panel may be affected by whether the solar receiver ispositioned high, low or centrally relative to those solar receivers. Itshould be appreciated that FIG. 3D is applicable only to some of theembodiments contemplated by the present invention and that the presentinvention contemplates other embodiments in which the reflector panelshave other curvatures, arrangements and/or shapes.

Referring next to FIGS. 4A and 4B, a collector unit 400 according to aparticular embodiment of the present invention will be described. Thecollector unit 400 may represent a stand alone structure, or it may beunderstood as a basic building block for many other designs. That is,multiple collector units 400 may be arranged together to form a widevariety of collector designs, some of which are described in FIGS. 5A-5Cand FIGS. 6A-6C. FIG. 4A illustrates a diagrammatic perspective view ofa collector unit 400 that includes one or more solar receivers 402 andone or more reflector panels 404. FIG. 4B illustrates a cross-sectionalview of the collector unit 400, which may also have any of the featuresdescribed in connection with FIGS. 2A-2C and 3A-3D. The collector unit400 is arranged such that the reflector panels 404 direct incidentsunlight 410 to the solar receivers 402. The reflected light forms aflux line on the receivers 402 that extends longitudinally down thelength of the collector unit.

As discussed previously with respect to other embodiments, the design ofthe collector unit 400 offers several advantages. Because the reflectivesurface of the reflector panels 404 is positioned in close proximity tothe solar receivers 402, the light need not traverse a long distancebetween the reflector panels 404 and the solar receivers 402, whichimproves mechanical and tracking tolerances for the collector.Additionally, the solar receivers 402 are positioned over a region justoutside a lower edge 406 of the reflective surface. As a result, thesolar receiver 402 (and any associated support structures) do not shadethe reflective surface and do not prevent incident sunlight fromreaching the reflective surface.

Some collector units involve multiple solar receivers and reflectorpanels that are arranged in rows that run parallel to one another alonga longitudinal axis. In the illustrated embodiment, for example,multiple longitudinally adjacent reflector panels 404 cooperate to forma reflector 408 with a substantially continuous reflective surface. Thesolar receivers 402 are also arranged longitudinally adjacent to oneanother to form a solar receiver row that extends in the longitudinaldirection 106. The length of the solar receiver row is generallysubstantially similar to that of the length L of the reflector. Invarious implementations, however, the solar receiver row may be somewhatlonger or shorter than the reflector. It should be appreciated thatalthough the figure illustrates ten solar receivers 402 in the solarreceiver row and seven reflector panels 404 forming the reflector,almost any suitable number or combination of solar receivers andreflector panels may be used.

Multiple collector units 400 may be arranged in a wide variety of waysto form different types of solar collectors. Some examples are providedin FIGS. 5A-5C. FIG. 5A illustrates a solar collector 500 made of twocollector units 400 a and 400 b in which the first and second reflectors502 a/502 b are arranged with their backsides to one another in atent-like arrangement. In the illustrated embodiment, the first andsecond reflectors 502 a/502 b are arranged substantially symmetricallyaround the center of the collector. A reflective surface on eachreflector 502 a/502 b has a parabolic or otherwise curved shape. Thefirst and second reflectors 502 a/502 b are arranged to form an A-likeshape, i.e. the inner edges 503 a/503 b of the reflectors 502 a/502 bare positioned adjacent to one another at the middle of the collector,the reflectors 502 a/502 b curve inward relative to one another, and theouter edges 506 a/506 b of the reflectors 502 a/502 b are positioned atthe periphery of the collector 500 and at a lower height than the inneredges 503 a/503 b of the reflectors 502 a/502 b. The first and secondsolar receivers 504 a/504 b are positioned above a peripheral regionoutside the outer edges 506 a/506 b of the first and second reflectors502 a/502 b, respectively, and are physically supported by receiversupport structures. An advantage of this implementation is the locationof the solar receivers 504 a/504 b at the periphery of the collector500, which allows easy access to the receivers for installation,cleaning and repair. Additionally, the solar receivers 502 a/502 b aresomewhat removed from other collector components, which may facilitateheat dissipation.

FIG. 5B illustrates a different way of arranging two collector units 400a/400 b. In the illustrated embodiment, the first and second reflectors522 a/522 b, which may have a curved or parabolic shape, aresubstantially symmetrically arranged and curve outward to form a trough-or U-like shape. That is, the inner edges 523 a/523 b of the reflectors522 a/522 b are positioned closer to the middle of the collector 520,while the outer edges 526 a/526 b of the reflectors 522 a/522 b arepositioned at the periphery of the collector 520. The outer edges 526a/526 b are positioned higher than the inner edges 523 a/523 b, whichresults in the formation of a U-type design. Two solar receivers 524a/524 b, whose respective photovoltaic cells face away from one another,are positioned over a central region between the inner edges 523 a/523 bof the reflectors 522 a/522 b. An advantage of this implementation isthat the two solar receivers 524 a/524 b are positioned at a singlelocation, which means that fewer structures are required to physicallysupport them then if they were separated across the width of thecollector 520.

FIG. 5C illustrates a collector 540 in which the collector units 400a/400 b are staggered at different heights. Rather than being arrangedside-by-side, the second solar receiver 544 b is positioned over andshades the first solar receiver 544 a. To maintain its proper alignmentwith the second solar receiver 544 b, the second reflector 542 b ispositioned higher than the first reflector 542 a. That is, the collector540 is generally symmetrical between the two collector units 400 a/400b, except that the collector units are offset along the vertical y axis112. An advantage of this design is that the solar receivers 544 a/544 btake up less space along the x axis 114. A review of FIG. 5C indicatesthat the pairs of solar receivers 524 a/524 b and 544 a/544 b of FIGS.5B and 5C take up a distance G and G′, respectively, which extends alongthe x axis 114. Because the two solar receivers 544 a/544 b in FIG. 5Care stacked over one another, the distance G′ of the collector 540 inFIG. 5C is substantially less than the distance G of the collector 520in FIG. 5B. As a result, the ratio of the reflective area of thecollector to the total area of the collector is increased, which meansthat for the same amount of real estate, more light is directed to thephotovoltaic cells of the collector 540 in FIG. 5C.

Referring next to FIGS. 6A-6C, extended solar collectors in accordancewith various embodiments of the present invention will be described.Each extended solar collector involves multiple collector units that arecoupled with a common base. The common base allows a larger number ofreflectors and solar receivers to be part of a single collectorstructure that can be pivoted to track the movements of the sun.

FIG. 6A relates to an extended collector 600 that is an extended versionof the A-type collector illustrated in FIG. 5A. That is, in addition tothe reflectors 502 a/502 b and solar receivers 504 a/504 b illustratedin FIG. 5A, the extended collector includes at least a third reflector502 c and a fourth reflector 502 d. The third and fourth reflectors 502c/502 d are positioned outside the outer edges of the first and secondreflector panels 502 a/502 b, respectively, and are oriented in asimilar manner (e.g., curving inwards towards a central region of thecollector, with the inner edges being higher than the outer edges.) Eachreflector has a reflective surface and an opposing backside surface. Thereflective surface of each reflector is arranged to direct incidentlight to one of the solar receivers. The first and second solarreceivers 504 a/504 b are positioned near the inner edges and on thebacksides of the third and fourth solar receivers 502 c/502 d,respectively. As a result, it is not necessary to use a separatestructure to support the solar receivers 504 c/504 d, since thereflectors 502 c/502 d can be used to hold the solar receivers inposition. In the illustrated embodiment, there are two more reflectorsand two more solar receivers in the collector beyond the ones describedabove, that essentially repeat the aforementioned receiver-reflectorarrangement (e.g., each reflector is arranged to direct sunlight to asolar receiver that is on the backside of the next reflector, except forthe solar receivers at the far ends of the collector 600.) It should beappreciated that fewer or more reflectors and solar receivers may beused. All of the reflectors and receivers are mounted on a common basestructure 602 that can be pivoted along at least one axis to trackincident sunlight.

FIG. 6B relates to an extended collector 620 that is an extended versionof the U-type collector 520 illustrated in FIG. 5B. That is, in additionto the reflectors 522 a/522 b and solar receivers 524 a/524 billustrated in FIG. 5B, the extended collector 520 includes at least athird reflector 522 c and a fourth reflector 522 d. The third and fourthreflectors 522 c/522 d are positioned outside the outer edges of thefirst and second reflectors 522 a/522 b, respectively, and are orientedin a similar manner (e.g., curving outwards away from a central regionof the collector, with the outer edges being higher than the inneredges.) Additional third and fourth solar receivers 524 c/524 d areattached with the backsides of the first and second reflectors 522 a/522b. The third and fourth reflectors 522 c/522 d are arranged to directincident light into the third and fourth solar receivers 524 c/524 d,respectively. The solar receivers 524 a-524 d and reflectors 522 a-522 dare mounted on a common base structure 604 that is arranged to pivot inorder to track movements of the sun. Additional reflector panels andsolar receivers may be attached with the common base structure 604 inthe manner of the third and fourth solar receivers 524 c/524 d and thethird and fourth reflectors 522 c/522 d to further expand the reflectivearea and power generating capacity of the solar collector 620.

FIG. 6C illustrates an extended collector according to anotherembodiment of the present invention. The features of the collector 640are almost identical to those of the collector 600 in FIG. 6A, exceptthat at least some of the reflectors 502 a-502 d are at differentheights. In the illustrated embodiment, for example, the collector 640is symmetrical along a bisecting axis 608 and the common base structure606 supports at least some of the reflectors on each side of thebisecting axis 608 such they are offset from one another along thevertical y axis 112.

It should be appreciated that FIGS. 5A-5C and 6A-6C provide only a fewof the possible arrangements of reflectors and solar receivers that arecontemplated in the present invention. Although most of the figuresinvolve substantially symmetrical collector designs, in some embodimentsthe designs may instead be asymmetrical. The reflector panels and solarreceivers of each solar collector may or may not have substantiallyidentical dimensions and/or shapes in the same collector. The commonbase structures 602/604/606 of FIGS. 6A-6C are drawn diagrammatically asplatforms with flat surfaces, but it should be appreciated that a basestructure may take a wide variety of forms, including a space framesupport structure, multiple separate support structures, etc.

Referring next to FIGS. 7A-7C, a space frame support structure 702 foruse in a solar collector 700 according to a particular embodiment of thepresent invention will be described. FIG. 7A illustrates a diagrammaticcross-sectional view of an U-type collector 700 (e.g., as described inFIGS. 1A-1B and 5A), which includes a space frame support structure 702that physically supports the solar receivers 706 a/706 b and thereflector panels 704 a/704 b. FIGS. 7B and 7C illustrate diagrammaticperspective views of the collector 700, with some of the reflectorpanels removed to reveal more of the underlying space frame. The spaceframe support structure 702 includes multiple struts that are connectedat nodes. The struts 708 include one or more receiver support struts 714a/714 b/714 c and one or more reflector support struts 712 a/712 b.

The space frame support structure 702 is arranged to disperse loadsoriginating at the solar receivers 706 a/706 b and the reflector panels704 a/704 b. In the illustrated embodiment, for example, the receiversupport struts 714 a/714 b/714 c are linear pipes, tubes, or cylindersthat extend diagonally out from a location immediately underneath thesolar receivers to one or more nodes within the space frame. As aresult, loads originating at the solar receivers are largely convertedinto compressive or tensile forces on one or more of the underlyingstruts, which are better tolerated. Additionally, the structures thatare supporting the receiver and reflector panels are not physicallyisolated from the rest of the rest of the space frame support structure,which may render them more vulnerable to bending or damage. Instead,components such as the receiver support structures are integrated intothe overall space frame support structure such that the loads from thesolar receivers are carried not only by the structures that are indirect contact with them, but also by the rest of the space framesupport structure. The space frame support structure 702 may be viewedas a unitary structure, since it supports and distributes the loads fromboth the solar receivers 706 a/706 b and the reflector panels 704 a/704b in an integrated or unitary fashion.

Various implementations involve a space frame support structure 702 thatis made of linear struts that are connected at nodes to form multiplegeometric shapes, such as pyramids, tetrahedrons, etc. These shapes helpto disperse stresses from carried components through multiple pathswithin the space frame. The space frame support structure has largeapertures 716 and internal spaces that allow the passage of air, whichsubstantially reduces wind load on the collector 700. The largeapertures 716 also facilitate cleaning of and access to the space framesupport structure 702 and are less likely to catch debris.

Generally, the space frame support structure 702 is arranged to minimizeor eliminate any shading of the reflector panels 704 a/704 b. In someembodiments, no portion of the solar receivers, the space frame supportstructure or any part of the solar collector shades the reflector panels704 a/704 b during the normal operation of the solar collector.

The space frame support structure may include multiple, longitudinallyextended longerons that form a base framework for the rest of the spaceframe support structure. The longerons may be continuous tubessubstantially equal in length to the collector length. The tubecross-section may be square, rectangular, circular, or some other shape.Struts are attached to nodes on the longerons to create an integrated,web-like, highly resilient structure. (The term “longeron” may beunderstood in the present application as any suitable type of linearmember that extends in a longitudinal direction.) For example, FIGS.7B-7C illustrate a space frame support structure 702 that includes anupper longeron 718, side longerons 720 and lower longerons 722. Eachlongeron is a linear member that extends along a longitudinal axis 106.The upper longeron 718 is arranged to physically support one or moresolar receivers 706 a/706 b. The side longerons 720 are positioned nearthe outer edges 724 of the reflector panels 704 a/704 b and mayindirectly help to support the panels. The lower longerons 722 arearranged at a bottom portion of the space frame support structure 702.All of the longerons extend substantially parallel to one another alongthe longitudinal axis 106.

Each of the longerons have multiple nodes that are separated by gaps andare distributed along the length of the longeron. The nodes areconnecting points for multiple additional struts that can cause forcesto be dispersed through multiple paths. For example, the upper longeron718 has multiple upper nodes 726 along its length. In some embodiments,each upper node 726 is adjacent to and directly underlies one or moresolar receivers 706 a/706 b, although this is not a requirement.Multiple receiver support struts 714 a/714 b/714 c extend diagonallydownward from each upper node 726 to help support the solar receivers706 a/706 b. While the upper longeron 718 may experience some bendingforce, the receiver support struts 714 are subject primarily to tensileor compressive loads. Force that is applied to the solar receivers 706a/706 b is dispersed through multiple, suitably angled receiver supportstruts 714 a/714 b/714 c, rather than a single support member.

The solar receivers 706 a/706 b may be attached at multiple points alongthe upper longeron 718. The attachment points may be located at regularintervals along the longeron. These attachment points need notcorrespond with space frame nodes. If the longeron is formed from arectangular tube, the attachment to the longeron may include a U-shapedchannel that fits over the longeron. Both the longeron and the U-shapedmay include holes. The U-shaped channel may be secured to the longeronby aligning these holes and inserting a fastener through the holes.

In some designs, the receiver support struts 714 fan out from the uppernodes 726 and connect to various nodes deeper within the space framesupport structure. By way of example, in FIG. 7A, one receiver supportstrut 714 b extends straight down and directly underneath the solarreceivers 706 a/706 b and is coupled to a central node 728 in the spaceframe support structure. Two other receiver support struts 714 a/714 cextend diagonally downward to lower nodes 730 a/730 b, respectively,which are coupled to the lower longerons 722 at the bottom of thecollector 700. In the illustrated embodiment, the lower nodes 730 a/730b are positioned below the reflector panels. While FIG. 7A illustratesthree receiver support struts 714 a/714 b/714 c extending out an uppernode 726, it should be appreciated that there may also be more or fewerreceiver support struts extending out of the upper node or any singlenode.

There are also multiple side nodes 732 that are separated by gaps andare distributed along the length of each side longeron 720. Multiplereflector support struts 712 a/712 b extend diagonally out from eachside node 732 to help physically support the reflector panels. One ofthese struts 712 a, which extends towards and is coupled to the sidelongeron 720, is coupled to the central node 728. Another is coupled tothe lower node 730 b and also extends to the side longeron 720. The tworeflector support struts 712 a/712 b are attached to the side longeron720 via the same side node 732.

The reflector support struts 712 a/712 b cooperate to form a base uponwhich the reflector panels 704 a/704 b may be positioned. Variousimplementations involve reflector support struts 712 a/712 b that extendin a direction substantially perpendicular to the upper and sidelongerons 718/720. To further facilitate the mounting of reflectorpanels 704 a/704 b to the space frame support structure 702, one or morestringers 734 may be positioned over the aforementioned receiver supportstruts 712 a. In the illustrated embodiment, for example, the stringers734 overlie and extend perpendicular to the receiver support struts 712a. Each stringer 734 includes one or more attachment points forattaching to an overlying reflector panel. The stringers 734 provideadditional stiffness to facilitate more accurate alignment of thereflector panel. Together with the reflector support struts 712 a/712 b,the stringers 734 also help to distribute the load of the reflectorpanels more evenly over the space frame. Generally, stringers 734facilitate the mounting of different sized reflector panels, since theymay be substantially invariant along the longitudinal direction,attachment points between the stringers and reflector panels may beinstalled at any location. In some embodiments, stringers are not usedand the reflector panel is attached with a different support member(e.g., a receiver support strut 712 a.)

The struts and nodes may take a wide variety of forms, depending on theneeds of a particular application. They may be made of almost anysuitably resilient material, such as aluminum or steel. For example,tubular aluminum extruded members, roll formed steel sections and hotrolled steel sections work well as struts in the space frame supportnetwork. The nodes may be understood as connecting points for multiplestruts. Struts can be connected at nodes without a connector (e.g., byform fitting or crushing the struts together, bending the struts aroundone another, fabricating through holes in one strut for the insertion ofanother strut, or any other suitable technique.) Welding, metalclinching, adhesive, rivets and bolts may be used to connect struts,connectors and/or nodes of the space frame support structure. In someembodiments, each node includes a separate connector that helps securethe incoming struts. The connector may take any suitable form, such as ametal sphere, a hub, etc. In some implementations, the connector isarranged such that the long axes of the incoming struts are arranged tomeet substantially at a single point within the node and/or connector.Struts may be attached to the connector using various mechanisms,including pins, fasteners, bolts, etc.

In the illustrated embodiment, the gap G between the reflector panels704 a/704 b is utilized to provide extra structural support for thesolar receivers 706 a/706 b. By widening this gap appropriately, roomcan be made for multiple receiver support structures 714 a-714 c thathelp to stabilize the position of the solar receivers. In any case, alarge portion of the gap G is covered by the solar receivers 706 a/706b, and thus cannot be used for the reflection of sunlight. In some priorart concentrating photovoltaic systems, this gap between the reflectorpanels 704 a/704 b is either non-existent or not wide enough toaccommodate a substantial support framework.

The length of the receiver support struts 714 a-714 c may be adjusted tohelp make the overall collector more symmetrical around its pivot axis736. That is, the upward extension of the receiver support struts 714a-714 c helps to balance out the lateral extension of the reflectorpanels 704 a/704 b. Thus, in various embodiments, the height h to widthw ratio of the collector 700 (as measured along a plane defined by the xaxis 114 and the y axis 112) is greater than approximately 0.4. A moresymmetrical arrangement helps reduce the buildup of stresses on aparticular portion of the space frame support structure, even when it isrotated to track movements of the sun.

Referring next to FIG. 7D, a solar collector according to anotherembodiment of the present invention will be described. FIG. 7D is adiagrammatic cross-sectional view of a solar collector 740 that includesa space frame support structure 742 with a different arrangement ofstruts, nodes and longerons than what was shown in FIGS. 7A-7C. Thespace frame support structure 742 includes side longerons 752, a singleupper longeron 754 and a single lower longeron 750. The upper longeron754, which is attached to one or more solar receivers 744 a/744 bthrough upper node 762, is supported by two receiver support struts 748a/748 b that extend diagonally down from the upper longeron 754 and arecoupled to two central nodes 756 a/756 b. Two additional struts 758a/758 b connect the central nodes 756 a/756 b with the single lowerlongeron 750 to form a diamond shape between the upper longeron 754 andthe lower longeron 750. In the illustrated embodiment, the collector 740is symmetrical along a bisecting plane 759, and both the upper and lowerlongerons 754/750 are on this bisecting plane 759. Multiple reflectorsupport struts 760 a/760 b are coupled to and extend from the centraland lower nodes 756 a/756 b/750 to each side longeron 752, where theyare attached to the side longeron 752 via the same side node 762.Similar to the space frame support structure 702 illustrated in FIG. 7A,the interconnections and structures illustrated in FIG. 7D may berepeated down the length of the longitudinally extended collector 740(e.g., there are multiple upper nodes and side nodes arranged along thelongitudinal lengths of the upper and side longerons, which may eachhave the same interconnections as described above.) A notable feature ofthis space frame design is that any node is limited to a relatively lownumber of connecting struts (e.g., in the case of FIG. 7D, only four.)For some applications, this feature is desirable, since it makes thenode somewhat easier to handle, install and repair.

It should be appreciated that there is almost an infinite number of waysto arrange the longerons, struts and nodes of the space frame supportstructure. FIGS. 7A-7D should be understood as merely exemplary andshould not be interpreted as limiting the range of space frame supportstructures that are contemplated in the present application.

The use of struts and nodes also makes the space frame support structurerelatively easy to ship and assemble. By way of example, individualstruts and nodes may be first compactly stored in a shipping containerso that they can be assembled almost entirely on-site. Alternatively,portions of the space frame support structure (e.g., interconnectednodes and struts that form a plane of the space frame support structure)may be preassembled prior to shipping. They may be preassembled inplanar trusses that can be assembled in the field. Some portions of thespace frame support structure (e.g., a planar combination of struts andnodes) may be arranged to be collapsible for shipment and fold out inthe field. In particular the planar trusses may be collapsible such thatthe struts are allowed to pivot about the nodes in such a way as for theplanar parts of the truss to collapse into a smaller volume. In anotherapproach, the main body of the space frame supporting structure may bepreassembled at the factory, and peripheral components are added onsite.

Referring next to FIG. 8A, a connector for use at a node of the spaceframe support structure according to a particular embodiment of thepresent invention will be described. FIG. 8A illustrates a connector 800that includes a body 802 and multiple connector fins 806. The body 802is arranged to accept a longeron 810, such as one of the longeronsdescribed in connection with FIGS. 7A-7D. Each connector fin 806 is asolid sheet or planar surface that extends out of the body 802.Preferably, the body 802 and fins 806 have simple geometries (e.g.,cylinders, planes, holes, slots, etc.) so that they are cost-effectiveto manufacture.

The body 802 of the connector 800 includes a feature for engaging alongeron 810 In the illustrated embodiment, for example, the body 802 isa hollow cylinder with open ends that is arranged to accept a longeron810. The body 802 may be secured to the longeron 810 using any suitablemeans, including a pin 814, a bolt, fastener, a latch, adhesive,welding, etc. If a pin is used, the pin may be stepped and the holediameter in the strut and connector appropriately sized so that each pinstep has substantially equal engagement with the hole in the strut orconnector.

Each fin 806 is arranged to securely engage one or more additionalstruts 808. This may be performed in a variety of ways. By way ofexample, each strut 808 may be a metal tube, bar, rod or cylinder whoseend has a slot 812. The edge of the fin 806 of the connector 800 isarranged to slide into the slot 812 of the strut 808. By lining upalignment holes 804 in the fin 806 and the end of the strut 808 andextending a pin 816 through the holes and the slot 812, the strut 808can be secured to the fin 806. Preferably, the struts 808 contact theconnect 800 at substantially different angles to avoid mechanicalinterference. In some embodiments, a connector 800 and its connectedstruts 808 are arranged such that the long axes of the incomingconnecting struts 808 meet at substantially the same point, which may ormay not be in the connector 800.

Referring next to FIGS. 9A-9B, a solar collector 900 with a space framesupport structure 902 according to another embodiment of the presentinvention will be described. FIG. 9A is a diagrammatic cross-sectionalview of a space frame support structure 902 suitable for use in A-typesolar collector, such as the one described in connection with FIG. 5A.FIG. 9B is a diagrammatic perspective view of the space frame spacestructure 902 illustrated in FIG. 9A. In the illustrated embodiment, thespace frame support structure 902 is substantially symmetrical along abisecting plane 904, although this is not a requirement. The solarcollector 900 is arranged to be rotated around pivot axis 921 to trackmovements of the sun.

The solar collector includes an upper longeron 910, two side longerons912 and two lower longerons 914 that extend parallel along thelongitudinal axis 106 of the solar collector 900. The upper longeron910, in contrast to the upper longeron 718 of the space frame supportstructure 702 of FIGS. 7A-7C, does not have attachment sites for solarreceivers. Multiple upper nodes 920 are separated by gaps and arrangedalong the length of the upper longeron 910. Multiple support struts 922a/922 b/922 c fan downward from each upper node 920. Each of thesestruts 922 a/922 b/922 c are connected to one of the lower nodes 924a/924 b/924 c. Reflector support struts 926 a/926 b also extend from theupper node 920 and help physically support and underlie the reflectorpanels 908 a/908 b.

The solar receivers 906 a/906 b are coupled to various attachment sitesthat are on each side longeron 912. The side longeron 912 is supportedby receiver support struts 928 a/928 b that are positioned at theperiphery of the solar collector 900. In the illustrated embodiment, forexample, each solar receiver is physically supported by a first receiversupport strut 928 a and a second receiver support strut 928 b. The firstreceiver support strut extends upward from a lower node 924 c to theside node 930. The second receiver support strut extends upward from aperipheral node 932 to the side node 930.

The above arrangement of nodes and support struts are repeated atvarious points along the length of the longerons and the space framesupport structure 902. That is, there are multiple upper nodes 920,which are separated by gaps, along the length of the upper longeron 910.Support structures 922 a-922 c fan downward from each of these uppernodes 920 in the manner described above. Similarly, there are side nodes930, separated by gaps, along the length of each side longeron 912.Receiver support struts 928 a/928 b extend diagonally downward from eachof these side nodes 930 to corresponding lower and peripheral nodes 924c/932. As a result, a lattice of interlocking struts and nodes is formedthat helps to prevent too much stress from building up on a narrowportion of the support structure.

Referring next to FIGS. 10A and 10B, a reflector panel 1000 suitable forcoupling to the space frame support structure according to a particularembodiment of the present invention will be described. FIG. 10A is adiagrammatic side view of the reflector panel 1000. FIG. 10B is adiagrammatic perspective view of the reflector panel 1000. The reflectorpanel 1000 may be understood as an enlarged view of one of the reflectorpanels illustrated in the previous figures. By way of example, thelength l of the reflector panel 1000 may correspond with the length l ofthe reflector panel 200 illustrated in FIG. 2A. The width w_(r) of thereflector panel 1000 may correspond with the width w_(r) of thereflector panel 300 illustrated in FIG. 3A. As previously discussed, thereflector panel 1000 may have a compound curvature e.g., a convexcurvature in a plane including the longitudinal axis 106, and a concavecurvature along a plane defined by the x and y axes 112/114. Thereflector panel has a reflective frontside 1002 and a backside 1003.

The backside 1003 of the reflector panel 1000 includes attachmentfeatures 1004 for coupling the panel to the space frame supportstructure. In various embodiments, for example, the attachment featuresare used to secure the reflector panel 1000 to the stringers 734illustrated in FIG. 7B. In still other embodiments, the attachmentfeatures are used to secure the reflector panel 1000 to a reflectorsupport strut or other support member. The attachment features may useany suitable means to securely fasten the backside 1003 of the reflectorpanel 1000 to the underlying support structure. By way of example, theattachment features 1004 may involve adhesive, glue pads, holes,fasteners or threaded screw holes.

The reflector panel 1000 may have a variety of different compositionsand dimensions, depending on the needs of a particular application. Anyreflective material, such as metalized glass, aluminum, etc, may be usedto form the reflector panel. The reflective panel 1000 may berectangular, curved, parabolic, flat, and/or arranged in the form ofrectangular sheets or longer strips (e.g., as shown in FIG. 3B). Invarious embodiments, all of the reflector panels of a particular solarcollector have the same dimensions and curvatures, although in otherembodiments the panels may differ in their shape and size.

Referring next to FIG. 11, a solar collector row 1100 according to aparticular embodiment of the present invention will be described. FIG.11 is a diagrammatic perspective view of a solar collector row 1100 thatincludes multiple solar collectors 1102 that have been arranged adjacentto one another along a longitudinal axis 106. Multiple mounting posts1106 form a stand, which physically support the solar collector row forpivotal motion 1104, are positioned at the ends and at various pointsalong the length of the collector row. The illustrated collectors may beany of the collectors described in the present application.

Preferably, the solar collectors 1102 are coupled together such thatthey pivot together in tandem to track movements of the sun. Couplingdevices (not shown) are positioned underneath adjacent collectors 1102to help link the collectors 1102 together. Some embodiments of thecollector include a space frame support structure with short tubeassemblies at the longitudinal ends of the collector, which are eacharranged to be connected with a coupling device. Each coupling device isin turn supported by one of the mounting posts 1106, which physicallysupports the solar collector row 1100. When torque is applied to one ofthe collectors, the torque is transferred through the coupling devicesmay rotate the entire solar collector row 1100. Various implementationsof this approach are described in U.S. patent application Ser. No.12/846,620, entitled “Manufacturable Dual Trough Solar Collector,” filedJul. 29, 2010, which is incorporated herein in its entirety for allpurposes.

The present invention also contemplates a power generation plant thatincludes multiple solar collectors 1102 and solar collector rows 1100.The solar collector rows 1100 may be arranged in any suitable manner(e.g., in an array, side by side in a parallel formation, etc.) In someembodiments, multiple solar collectors 1102 are positioned on a commoncarousel type platform that can be rotated to track movements of thesun. All the collectors on the carousel rotation axis may rotate about acommon rotation axis. The rotation axis may be substantially vertical.In various embodiments, the collector longitudinal axes may lie in asubstantially horizontal plane, or the collector longitudinal axes mayhave a fixed, oblique tilt angle relative to the rotation axis.Alternatively, the collectors may be rotated about two axes. Suchapproaches are described in greater detail in U.S. patent applicationSer. No. 12/642,704, entitled “High Ground Cover Ratio Solar CollectionSystem,” filed Dec. 18, 2009, which is hereby incorporated in itsentirety for all purposes.

Referring next to FIG. 12, the tracking and pivoting of a solarcollector or solar collector row according to a particular embodiment ofthe present invention will be described. FIG. 12 is a diagrammatic endview of solar collectors 1102 that are at the ends of two of the solarcollector rows 1100 illustrated in FIG. 11. The two solar collector rows1100 are arranged in parallel and extend in a longitudinal direction(i.e., into the page). A mounting post 1204 physically supports eachsolar collector for pivotal movement around a pivot axis 1206 that alsoextends in the longitudinal direction. The mounting posts 1204 may beanchored into the ground or a common base 1210 (e.g., a roof top, carpark cover, etc.) A tracking system is arranged to pivot the solarcollector to track the movements of the sun, such that the incomingsunlight 1212 is substantially incident on the optical aperture of thecollector 1102.

Various designs involve a pivot axis 1206 that substantially passesthrough the center of gravity of each collector in a solar collector row1100. That is, the weight of the various components of the collector1102 are distributed evenly around the pivot. As a result, less force isrequired to rotate the collector 1102. The location of the center ofgravity of the collector 1102 depends on the weights of the variouscomponents. By way of example, it may be located along a bisecting plane1216 of the collector and/or between the reflector panels 1214 a/1214 b.Some embodiments involve adding weights to the bottom of the collector1102 to push the center of gravity lower. An economical and simple wayto do so is to fill some of the lower struts or longerons with solidmaterial, such as gravel, cement, sand, earth or steel balls.

The solar collector 1102 is arranged to accommodate a wide range ofmotion around the pivot axis. In some embodiments, for example, thetracking system, stand and solar collector 1102 are arranged to pivotthe solar collector at least 170 degrees, or at least 160 degrees, or atleast 150 degrees, while keeping the pivot axis 1206 substantially atthe center of gravity of the collector. Some implementations involve apivot range of at least 120 or 140 degrees. The pivot range can beincreased by pushing the pivot axis 1206 further from the center ofgravity. The pivot range may be adjusted to be lower or higher,depending on the solar insulation characteristics of a particular solarpower plant site.

Referring next to FIGS. 13A-13B, a solar collector 1300 with a supportcable 1306 according to a particular embodiment of the present inventionwill be described. FIG. 13A is a diagrammatic cross-sectional view ofthe solar collector 1300, which may be understood as the A-typecollector 500 illustrated in FIG. 5A. A support cable 1306 extendsacross the span of the collector 1300 to couple together the solarreceivers 1302 a/1302 b and/or the receiver support struts 1308 oneither side of the collector. FIG. 13B is a diagrammatic perspectiveview of the solar collector illustrated in FIG. 13A.

The support cable 1306 is arranged to provide additional support for thesolar receivers 1302 a/1302 b and their associated support structures.Preferably, the support cable 1306 has a small diameter so that it onlyminimally shades the underlying reflector panels 1304 a/1304 b. Forexample, a diameter of less than approximately 3 mm works well forvarious applications. Moreover, the effect of any shading by the cable1306 on the reflector panel can be further reduced if the reflectivepanel has a convex curvature. That is, even when portions of thereflective panel are rendered unable to reflect light, there may be fewor no breaks in the flux line formed by the reflective panel, for thereasons previously discussed in connection with FIGS. 2A-2C.

The support cable 1306 may be made of any suitably resilient material,such as a metal wire. It may be attached directly to opposing solarreceivers 1302 a/1302 b, to a portion of the support structure for thesolar receivers, are some other suitable portion of the collector 1300.Various embodiments of the present invention involves a support cable1306 that extends diagonally multiple times across the span of thecollector (e.g., as seen in FIG. 13B), rather than directly across(e.g., in a direction that is perpendicular to the longitudinal axis 106of the collector.)

Although only a few embodiments of the invention have been described indetail, it should be appreciated that the invention may be implementedin many other forms without departing from the spirit or scope of theinvention. In the foregoing description, components in one figure can bemodified or replaced based on corresponding elements in another figure.For example, the features of the reflector panel 1000 illustrated FIG.10 may be included in any figure that references a reflector panel,including but not limited to FIGS. 1A, 2A-2C and 3A-3D. It should alsobe noted that the axes may be understood as having a consistent meaningacross all the figures. That is, the x, y, and z axes are perpendicularto one another. Additionally, it should be noted that the axes may beused to understand the design of various embodiments that are based onmore than one figure. For example, FIG. 2B illustrates a line of convexshaped reflector panels that extend along a longitudinal axis. FIG. 1Billustrates a relatively zoomed out view of a collector in which thepanels are illustrated in less detail. Therefore, the present inventionalso contemplates a particular embodiment where the features of thereflector panels of FIG. 2B are included in the reflector panels of FIG.1A. In understanding this embodiment, the longitudinal axes 106 of FIGS.1A and 2B may be used as a common reference point to understand how thereflector panels of FIG. 2B are used in the collector of FIG. 1A.Additionally, the specification and claims sometimes refer to “thenormal operation of the solar collector.” This generally refers to amode in which the collector is tracking the movement of the sun (e.g.,as shown in FIG. 12). However, it should be appreciated that thecollector does not necessarily always track the sun during normaloperation. For example, in some implementations the collector does nottrack the sun in the early morning. Therefore, the present embodimentsshould be considered as illustrative and not restrictive and theinvention is not limited to the details given herein, but may bemodified within the scope and equivalents of the appended claims.

1. A photovoltaic solar energy collector suitable for use in a solarenergy collection system that includes the collector, a stand thatsupports the collector and a tracking system that causes the collectorto track movements of the sun along at least one axis, the collectorcomprising: at least one reflector panel that extends in a longitudinaldirection; at least one solar receiver, each solar receiver including atleast one photovoltaic cell, the at least one reflector panel beingarranged to direct incident sunlight to the at least one solar receiver;and a space frame support structure that physically supports the atleast one reflector panel and the at least one solar receiver, the spaceframe support structure including a multiplicity of linear struts thatare connected at nodes to form a multiplicity of triangular structures;including a first triangular structure and a second triangular structurewherein: the first triangular structure is arranged to help physicallysupport the at least one solar receiver and includes first, second andthird vertices, the first vertex of the first triangular structure beingadjacent to and underlying the at least one solar receiver; and thesecond triangular structure is arranged to help physically support theat least one reflector panel and includes first, second and thirdvertices, the first vertex of the second triangular structure beingpositioned at the periphery of the collector wherein the second vertexof the second triangular structure is the second vertex of the firsttriangular structure.
 2. A solar collector as recited in claim 1,further comprising: a longeron that extends in said longitudinaldirection, the at least one solar receiver being attached with thelongeron; the nodes of the space frame support structure include aplurality of nodes that are separated by gaps and that are arrangedalong the length of the longeron; and a plurality of the struts arecoupled to each of the nodes on the longeron and extend diagonallydownward from the node to help support the at least one solar receiver.3. A solar collector as recited in claim 1, wherein: the at least onereflector panel includes a first reflector panel and a second reflectorpanel, the first and second reflector panels each including an inneredge and an outer edge that extend in a longitudinal direction, theinner edges of the first and second reflector panels being positionedcloser to one another than the outer edges of the first and secondreflector panels, the first and second reflector panels being arrangedsuch that the outer edges of the first and second reflector panels arepositioned higher than the inner edges of the first and second reflectorpanels; and the first and second solar receivers are positioned adjacentto one another over a region that is between the inner edges of thefirst and second reflector panels, respectively.
 4. A solar collector asrecited in claim 3, wherein: the collector further comprises a upperlongeron, the multiplicity of struts including at least two receiversupport struts that help physically support the at least one solarreceiver, the upper longeron being positioned higher than the first andsecond reflector panels and extending in said longitudinal direction,the first and second solar receivers being mounted on the upperlongeron; the nodes of the space frame support structure includes aplurality of top nodes that are separated by gaps and that are arrangedalong the length of the upper longeron, the top nodes being positionedhigher than the first and second reflector panels; and the at least tworeceiver support struts are attached to the top node on the upperlongeron and extend diagonally downward therefrom to pass between thefirst and second reflector panels to help support the first and secondsolar receivers.
 5. A solar collector as recited in claim 3, wherein:the second solar receiver is positioned over and shades the first solarreceiver; and the second reflector panel is positioned higher than thefirst reflector panel.
 6. A solar collector as recited in claim 3,wherein: the at least one reflector panel further includes a thirdreflector panel and a fourth reflector panel, each reflector panelhaving a backside and a reflective frontside, the third reflector panelbeing positioned outside the outer edge of the first reflector panel,the fourth reflector panel being positioned outside the outer edge ofthe second reflector panel, each reflector panel having a concave shapethat curves outward from a central region between the first and secondreflector panels; and the at least one solar receiver further includes athird solar receiver and a fourth solar receiver, the third and fourthsolar receivers being positioned on the backsides of and at the outeredges of the first and second reflector panels, respectively, whereinthe reflective frontsides of the third and fourth reflector panels arearranged to direct incident light to the third and fourth solarreceivers, respectively.
 7. A solar energy collector as recited in claim1, wherein: the nodes of the space frame support structure includes acentral node; the multiplicity of struts includes at least one reflectorsupport strut that physically helps to support the at least onereflector panel; the collector further comprises an upper longeron, alower longeron and a side longeron that all extend substantiallyparallel to one another in a longitudinal direction, the upper longeronbeing positioned higher than the lower longeron, the at least one solarreceiver being positioned on the upper longeron; and the at least onereflector support strut includes a first reflector support strut and asecond reflector support strut, the first reflector support strutextending from the central node in the space frame support structure tothe side longeron, the second reflector support strut extending from thelower longeron to the side longeron, wherein the first and secondreflector support struts are arranged to help physically support the atleast one reflector.
 8. A solar energy collector as recited in claim 1,wherein: each node in the space frame support structure includes aconnector for connecting a plurality of the struts, the connectorcomprising a base structure and at least one fin that extends out of thebase structure, each fin having at least one alignment hole; and aplurality of the struts each have a slot at one end and a plurality ofalignment holes, wherein the engagement feature is arranged to fitwithin the slot at the end of the strut and to be secured to the finwith a fastener that slides through the alignment holes of the strut andthe fin.
 9. A solar collector as recited in claim 1, wherein thelongitudinal period of the repeating geometric pattern does not equalthe longitudinal length of either a receiver or reflector panel.
 10. Aphotovoltaic solar energy collection system, comprising: a solarcollector as recited in claim 1; a stand that pivotally supports thecollector for pivotal movement around a pivot axis, wherein the pivotaxis passes substantially through the center of gravity of thecollector; and a tracking system that causes the collector to pivotaround the pivot axis to track movements of the sun along at least oneaxis.
 11. A solar energy collection system as recited in claim 10,wherein the range of motion around the pivot axis is one selected from agroup consisting of: 1) at least 150 degrees; 2) at least 160 degrees;and 3) at least 170 degrees.
 12. A solar energy collection system asrecited in claim 1, wherein each strut is formed from one selected froma group consisting of roll formed steel sections, hot rolled steelsections, and tubular aluminum extruded members.
 13. A solar energycollection system as recited in claim 1, wherein: the collector furthercomprises an upper longeron that extends along the longitudinal axis anda connector, the connector being an integrally formed metal piece thatencircles and is secured to the upper longeron, the connector havingengagement features for receiving the at least two receiver supportstruts; the multiplicity of struts includes at least two receiversupport struts, the at least two receiver support struts being arrangedto physically help support the at least one solar receiver, the at leasttwo receivers support struts being secured to the connector on thelongeron and extending diagonally downward from the upper longeron atleast partially in a direction that is perpendicular to the longitudinalaxis, thereby helping to physically support the upper longeron and thefirst and second solar receivers; the solar collector is substantiallysymmetrical along a bisecting plane; and the upper longeron and theattached connector are positioned on the bisecting plane, are adjacentto and underlie a region that is between the first and second solarreceivers.
 14. A photovoltaic solar energy collector suitable for use ina solar energy collection system that includes the collector, a standthat supports the collector and a tracking system that causes thecollector to track movements of the sun along at least one axis, thecollector comprising: at least one reflector panel that extends in alongitudinal direction; at least one solar receiver, each solar receiverincluding at least one photovoltaic cell, the at least one reflectorpanel being arranged to direct incident sunlight to the at least onesolar receiver; and a space frame support structure that physicallysupports the at least one reflector panel and the at least one solarreceiver, the space frame support structure including a plurality oflongerons and a multiplicity of linear struts that are connected atnodes to form a repeating geometric pattern, the space frame supportstructure being unitary such that both receiver and reflector loads aredistributed through the space frame support structure, wherein there isa connector at least some of the nodes, each connector comprising: ahollow, open-ended body that is arranged to engage and encircle one ofthe longerons; and a plurality of fins that extend out of the body, eachfin including at least one alignment hole, wherein the ends of at leastsome of the struts include a slot, each fin being arranged to beinserted into the slot to help secure the fin to the strut.
 15. Aphotovoltaic solar energy collector as recited in claim 1 wherein thecollector supports adjustable attachment points for attaching the atleast one reflector panel such that different numbers of reflectorpanels and reflector panels of different sizes can be mounted on thespace frame support structure.
 16. A photovoltaic solar energy collectoras recited in claim 1 wherein: the at least one reflector panel has aconcave shape; the multiplicity of linear struts includes a plurality ofreflector support struts that underlie, are adjacent to and physicallysupport the at least one reflector panel wherein the plurality ofreflector support struts are straight and do not match the concave shapeof the reflector panel.
 17. A photovoltaic solar energy collector asrecited in claim 1 wherein each of the multiplicity of triangularstructures are formed from at least three of the linear struts andwherein the at least three of the linear struts define and border anaperture in a central region of the triangular structure that allows airto pass therethrough.
 18. A photovoltaic solar energy collector asrecited in claim 1 wherein: there is a gap between the first and secondreflector panels; a plurality of the linear struts, which form at leastpart of the first triangular structure, extend through the gap betweenthe first and second reflector panels and meet at a top node, whichforms the first vertex of the first triangular structure; there is anaperture between the plurality of linear struts of the first triangularstructure that allows air to pass therethrough; and the top node issituated higher than the first and second reflector panels and isadjacent to the first and second solar receivers.
 19. A photovoltaicsolar energy collector as recited in claim 1 wherein the third vertex ofthe first triangular structure is the third vertex of the secondtriangular structure.
 20. A photovoltaic solar energy collector asrecited in claim 14 wherein at least one of the plurality of finsincludes a plurality of alignment holes and is thereby arranged to besecured with a corresponding plurality of the struts.